1. Field of Invention
Exemplary aspects of the present invention relate to an image forming apparatus, and more particularly to an image forming apparatus that includes a coupling device for effectively connecting a drive-side coupling and a driven-side coupling even if shaft centers of the drive-side coupling and the driven-side coupling are misaligned.
2. Discussion of the Background
A related art coupling device 500A illustrated in FIG. 1 includes a drive-side coupling 502A serving as a first coupling and a driven-side coupling 501A serving as a second coupling. The drive-side coupling 502A is disposed on a tip surface of a drive-side base 503A serving as a first base. A plurality of driving claws 504A serving as first claws (one drive claw is shown in FIG. 1) are integrally formed with the drive-side base 503A. The driven-side coupling 501A is disposed on a tip surface of a driven-side base 506A serving as a second base. A plurality of driven claws 507A serving as second claws are integrally formed with the driven-side base 506A. As shown in FIG. 1, in a state where the drive-side coupling 502A and the driven-side coupling 501A are connected, each of the driving claws 504A and the driven claws 507A are alternately positioned, meshing each driving claw 504A with each driven claw 507A. The drive-side coupling 502A is connected to a driving shaft 508A. As the driving shaft 508A is rotatively driven by a not-shown driving source, the drive-side coupling 502A rotates. Accordingly, the driving claws 504A and the driven claws 507A are pressed with one another, and the rotation of the drive-side coupling 502A is transmitted to the driven-side coupling 501A, rotating a driven shaft 509A which is secured to the driven-side coupling 501A, thereby rotatively driving a rotation element of a driven unit 510A (not shown).
The driven-side coupling 501A is detachably connected with respect to the drive-side coupling 502A in a shaft line direction Z1 of the drive-side coupling 502A. By moving the driven-side coupling 501A together with the driven unit 510A in an arrow A-direction, the driven-side coupling 501A may be disengaged from the drive-side coupling 502A. On the other hand, by pressing the driven-side coupling 501A together with the driven unit 510A in an arrow B-direction, the driven-side coupling 501A and the drive-side coupling 502A are connected.
The drive-side coupling 502A is connected such that it is movable for a specific number of strokes in a shaft line direction Z1 with respect to the driving shaft 508A. Furthermore, a compression spring 512A is disposed between a spring receiving part 511A secured to the driving shaft 508A and the drive-side coupling 502A.
In a case where top faces 513A of the driven claws 507A collide with top faces 514A of the driving claws 504A when the driven-side coupling 501A is pressed in the arrow B-direction, the drive-side coupling 502A is pressed by the driven-side coupling 501A. Consequently, the drive-side coupling 502A moves in the arrow B-direction with respect to the driving shaft 508A, and the compression spring 512A is compressed. In this state, when the drive-side coupling 502A rotates, the driving claws 504A rotate with respect to the driven claws 507A, and due to the pressure effect of the compression spring 512A, the drive-side coupling 502A moves in the arrow A direction. As a result, each of the driving claws 504A advances between each of the driven claws 507A so that each of the driving claws 504A and each of the driven claws 507A are alternately positioned in a peripheral direction of the coupling device 500A. Accordingly, each of the driving claws 504A and each of the driven claws 507A are engaged, and the rotation of the drive-side coupling 502A is transmitted to the driven-side coupling 501A.
As described above, even if the top faces 513A of the driven claws 507A collide with the top faces 514A of the driving claws 504A when the driven-side coupling 501A and the drive-side coupling 502A are connected, the driven claws 507A and the driving claws 504A may be engaged by the rotation of the drive-side coupling 502A.
However, in the above-described coupling device 500A, the compression spring 512A is needed so that the driven claws 507A and the driving claws 504A are engaged even if the top faces 513A of the driven claws 507A collide with the top faces 514A of the driving claws 504A. Consequently, it results in a growing number of parts to be used for the coupling device 500A. Moreover, a space in which the compression spring 512A is disposed is needed, thereby increasing the size of an entire coupling device 500A.
In view of this, Japanese Laid-Open Patent Application 2005-76873, for example, proposes a coupling device in an effort to address this problem. FIG. 2 is a schematic diagram of the coupling device 500B proposed in Japanese Laid-Open Patent Application 2005-76873. FIG. 3 is a perspective view of the coupling device 500B. As shown in FIG. 2, the coupling device 500B includes a drive-side coupling 502B and a driven-side coupling 505B. The drive-side coupling 502B includes a cylindrical drive-side base 503B which is secured to a driving shaft 508B. A plurality of driving claws 504B are disposed on an outer peripheral surface of the drive-side coupling 502B. The driven-side coupling 505B includes a cylindrical driven-side base 506B, which is secured to a driven shaft 509B. A plurality of driven claws 507B are disposed on an inner peripheral surface of the driven-side base 506B. As shown in FIG. 3, on a tip portion of each of the driving claws 504B are formed slant faces 536B. Tips 538B of each of the driving claws 504B are linearly extended along a normal line from the drive-side base 504B. On a tip portion of each driven claws 507B are formed the slant faces 536B slanted in the same direction when facing each driving claw 504B. Accordingly, tips 535B of each of the driven claws 507B are linearly extended from the driven-side base 506B to a shaft center.
In a case where the driven claws 507B and the driving claws 504B come into contact when the driven-side coupling 505B is connected to the drive-side coupling 502B, the slant faces 535B of the driven claws 507B come into contact with the slant faces 536B of the driving claws 504B. When the slant plates 535B of the driven claws 507B and the slant faces 536B of the driving claws 504B come into contact, pressure force in which the driven-side coupling 505B is pressed in the shaft direction is dispersed to the rotation direction and the shaft direction. Consequently, if the driven-side coupling 505B continues to be pressed in the shaft direction, the slant faces 535B of the driven claws 507B and the slant faces 536B of the driving claws 504B slide along one another, rotating either one of the driven-side coupling 505B or the drive-side coupling 502B. As a result, each of the driven claws 507B advances between each of the driving claws 504B so that each of the driving claws 504B and each of the driven claws 507B are engaged.
In the coupling device 500B proposed in Japanese Laid-Open Patent Application 2005-76873, without the compression spring 512A, the driven claws 507B and the driving claws 504B may be engaged, even if the driven claws 507B and the driving claws 504B come into contact when the driven-side coupling 505B is connected to the drive-side coupling 502B. As a result, a number of parts and the size of the apparatus may be reduced.
FIG. 4 illustrates the way a driven unit 510B, including the driven-side coupling 505B of the coupling device 500B, is attached to a rear plate 516B. As illustrated in FIG. 4, a hole 517B through which a shaft 511B of the driven-side unit 510B is inserted is provided on the rear plate 516B. When the driven unit 510B is mounted in the apparatus main body, the driven unit 510B is shifted in the shaft direction so as to insert the shaft 511B into the hole 517B and determine the position of the driven unit 510B. Subsequently, the driven-side coupling 505B and the drive-side coupling 502B are connected. In a case where the driven-side coupling 505B and the drive-side coupling 502B are connected after the position of the driven unit 510B is determined, there is a possibility that the shaft center of the drive-side coupling 502B and the shaft center of driven-side coupling 502B are misaligned. That is, because the position of the driven unit 510B is determined in advance, parts accuracy, accumulation of dimensional tolerance of the hole 517B or the like, and deflection due to unit stiffness may cause misalignment of the shaft centers.
FIG. 5 illustrates the driven-side coupling 505B seen from an E-direction of FIG. 2, and a dash-double dotted line in FIG. 5 indicates the drive-side coupling 502B. As illustrated in FIG. 5, in a case where the shaft centers of the drive-side coupling 502B and the driven-side coupling 505B correspond, the linear tips 538B of the driving claws 504B are parallel with the linear tips 540B of the driven claws 507B. As illustrated in FIG. 5, in a case where the linear tips 538B of the driving claws 504B are parallel with the linear tips 540B of the driven claws 507B, the driven-side coupling 505B is connected to the drive-side coupling 502B without the linear tips 538B of the driving claws 504B hitting the linear tips 540B of the driven claws 507B.
On the other hand, as shown in FIG. 6, in a case where the shaft centers of the drive-side coupling 502B and the driven-side coupling 505B are misaligned, as marked by the line X in FIG. 6, the linear tips 538B of the driving claws 504B and the linear tips 540B of the driven claws 507B will cross. In other words, because both tips of the driving claws and the driven claws are linear, when the shaft centers are misaligned, the angle of the tips 538B of the driving claws 504B and the angle of the tips 540B of the driven claws 507B will not correspond, thereby making the tips 538B of the driving claws 504B and the tips 540B of the driven claws 507B crossed. Accordingly, when the driven-side coupling 504B is connected to the drive-side coupling 502B while the shaft centers of the drive-side coupling 502B and the driven-side coupling 505B are misaligned, the linear tips 540B of the driven claws 507B will collide with the linear tips 538B of the driving claws 504B, and the driven-side coupling 505B may not be moved to the drive-side coupling. As a result, there is a problem that the driven-side coupling 505B and the drive-side coupling 502B may not be connected. In addition, when forcibly trying to connect the driven-side coupling 505B and the drive-side coupling 502B while the driving claws and the driven claws are collided, this may cause a distortion or damage to the tips of claws or the driven-unit 510B.